The biochemical control mechanisms underlying the secretion of mediators of immediate hypersensitivity will be investigated using isolated normal rat mast cells. The central approach of this work will be to better characterize the pharmacologic and immunologic modulation of cyclic nucleotides in mast cells. The changes in cyclic nucleotides during mediator release have been characterized: the enzymes involved in cyclic nucleotide metabolism will now be better characterized and the subcellular distribution of these enzymes and the cyclic nucleotide dependent and independent protein kinases and phosphorylases will be characterized and attempts will be made to demonstrate changes in protein phosphorylation during induction of mediator secretion. In addition, the role of calcium in mediator release, and the mechanisms of termination of the release process will be investigated including particular attention to possible effects on cyclic nucleotide metabolism. The role of phospholipid metabolism in mast cell secretion will be studied and the relation of the cyclic nucleotide systems to phospholipid metabolism will be studied. These results will be important in helping to clarify the mechanisms by which cyclic nucleotides and other regulatory molecules modulate or mediate mast cell secretion.